Mealybugs are related to scale insects, so if your plants have suffered from an infestation of this destructive insect, you can imagine the damage their cousin--the mealybug--can do. Mealybugs are small pink tropical insects, no larger than 1/5 inch long. They are covered with a waxy substance that looks like cotton. They attack not only the leaves of basil and other plants, but can also affect the roots. The University of Wisconsin reports that mealybugs cause "stunting, chlorosis, defoliation and wilting" of plants. If your basil has mealybugs, you'll want to control them before they destroy your plants.
Control the ants that bring mealybugs to your basil. Ants feed off these insects' excretion, which is a sweet substance called honeydew. First, spray your plants with a strong jet of water to remove as many ants and mealybugs as possible. Allow your basil plants to dry and then spread a layer of a product called Tanglefoot around the base of your basil plants and the ants won't be able to pass beyond it. You can also use ant baits or stakes if you don't mind using poisons around your basil.
Hang yellow sticky traps on and near your basil. The flying adult males will be attracted to these traps and will die after they become ensnared in the sticky substance.
Spray your basil with insecticidal soap, available as a concentrate or a pre-mixed spray at garden supply stores. Be sure to spray the undersides of the leaves where mealybugs can hide because this product must come into direct contact with the insects in order to be effective.
Introduce beneficial insects, such as green lacewings, which will eat the mealybugs. See Resources for an online source for ordering lacewings.